I think it was david that said Cisco's version of SMLT is better than Nortel's because the two Cisco Routers are seen as one device/config to the rest of the Network.
Nortel's SMLT technology works like this.

Two chassis with an InterSwitch Trunk between them. This IST allows the rest of the network to see one virtual switch (though they are really two physical boxes with the same configuration).
Now you have an MLT or LACP to another switch. The MLT (assuming it's only two links) is split between these two physically separate switches (one virtual switch). Nortel's MLT hashing algorithm determines which link to send frames down (based on src-dst mac addr). With VRRP-v2 (and Nortel's tweaks) configured (not mandatory for this design) you have what is called Backup-Master. If Backup Master is enabled, you have two active switches.
Another commenter mentioned that this is still VRRP (which is very true). VRRP is chatty (sending hello's every second with the option to send every 200ms!).
Nortel has tweaked VRRP a little more, taking the Chattyness out of it and creating RSMLT.
With RSMLT you get Active Active physically separate switches (one virtual) just like the VRRP design I explained but without all the hello's.
The writer of this article titled the article "smashes 'throughput records.' That caught my eye because I've read equipment specs and only Nortel can give you 2TBps throughput (within the chassis).
Cisco is great with all of it's automation features but throughput is weak in most cisco gear. They stick to software...Nortel will stick to hardware.